The invention relates to a decorative burnish gold composition containing gold powder and/or sparingly soluble gold compound for the decoration of glasses, especially drinking glasses.
Liquid polishing (burnish) gold, made of gold powder suspended in an oily medium, a flux promoting adhesion to the ceramic body and usually containing bismuth and chromium in the form of the resinate and the sulforesinate, respectively, and rhodium sulforesinate, is a preparation that has long been used in the ceramic industry for gilding (see, for example, F. Chemnitius, Sprechsaal 1927, pp. 182-184).
Instead of gold powder, a polishing gold, which after firing appears first as a dull gold coating, but after polishing becomes a silky, shiny coating, may also contain sparingly soluble gold compounds.
For example, German Pat. No. 1,286,866 discloses polishing gold preparations containing thermally degradable gold mercaptides, and German Pat. No. 2,111,729 discloses screeen printing pastes containing gold(III) sulfide.
In a polishing gold suitable for application to glass, lead borate and bismuth subnitrate are used as flux in one case, and a mixture of rhodium, bismuth and chromium resinates and sulfurated balsam in another, in German Pat. No. 1,286,866.
Additional fluxes contained in polishing gold preparations for glass, ceramic and porcelain consist of lead borosilicate or bismuth compounds (Canadian Pat. No. 546,066), and of lead, bismuth and silicon resinates (British Pat. No. 721,906).
A great number of fluxes are known for other gold and noble metal decorating compositions. For example, in the bright gold preparations described in U.S. Pat. No. 2,842,457 for application to glass and porcelain, bismuth, rhodium and vanadium or chromium resinates and sulforesinates are used. In the preparations described in German Pat. No. 1,421,865 for the production of coatings containing bright noble metal on glass ceramic objects, use is made, for example, of resinates, sulforesinates or alcoholates of a fluxing element. A series of such elements is listed therein.
Polishing golds for application to glass, which permits only relatively low firing temperatures (about 500.degree. to 650.degree. C.), usually contain lead fluxes.
However, inasmuch as a large part of the lead contained in decorating gold coatings goes into solution, as it is indicated by determining the solubility of lead in dilute acetic acid in accordance with DIN Standard 51031, the maximum amount of lead which can be dissolved out of drinking vessels, as established by DIN Standard 51032, is reached or even exceeded in drinking glasses decorated with a relatively narrow gold rim.